I want to pressurize a cryogenic liquid (LN2 in this test. Eventually LOX). I have a setup similar to this and follow a similar procedure to what is described, but I don’t see the same tank pressure behavior.
Instead, the curve looks like this, where “set pressure” is the pressure reading just after the pressurant regulator set to 700psi. T=12 is when the pressurization begins. T=40 is when expulsion begins. A check valve is in place so no gas flows back into the pressurant bottle. Notice how the tank pressure does not level-off at equilibrium at T=22. Tank pressure will continue to rise beyond, and I started expulsion before it could rise too high. It was observed previously that if I did not start expulsion it could rise past 1100psi.
Any idea what is going on? I am aware of “collapse factor” of pressurants for cryogens but the behavior should not be dissimilar from the first picture.